1. Field of the Invention
The present invention relates to a digital recorder which is capable of recording, reproducing and editing an audio signal in a digital fashion.
2. Description of the Related Art
For recording, reproducing and editing an audio signal, a method has been conventionally used, of recording an analog audio signal on a magnetic tape, reproducing the same from the magnetic tape and editing the recorded signal. Since the prior art involves an analog recording and reproducing process, deterioration of the sound quality is inevitable. Particularly, deterioration is prominent when the once-recorded audio signal is dubbed.
The use of the magnetic tape as a recording medium raises other problems that it takes time to reach a target editing point on the magnetic tape, and editing requires that a target recorded portion of the magnetic tape be physically cut and pasted or be copied to somewhere else before executing the editing.
The problem about the deterioration of the sound quality can be overcome by employing a method of digitally recording data on a magnetic tape. However, there still remains a shortcoming concerning the freedom of locating the starting point or editing due to the use of a sequential-access type recording medium.
Recently, there have been proposed solutions to the conventional problems which use a hard disk or a magneto-optical disk as a memory medium for disk-recording a digital signal such as the above mentioned audio signal, a video signal or a musical instrument digital interface (MIDI) signal.
For example, the following U.S. Patent applications have proposed several solutions to these conventional problems:
U.S. Ser. No. 07/690,710 filed Apr. 24, 1991, abandoned Inventor: Nobuo IIZUKA;
U.S. Ser. No. 07/752,876 filed Aug. 30, 1991, pending Inventor: Atsushi MIYAKE;
U.S. Ser. No. 07/795,983 filed Nov. 22, 1991, abandoned Inventor: Nobuo IIZUKA;
U.S. Ser. No. 07/807,053 filed Dec. 12, 1991, abandoned Inventor: Nobuo IIZUKA;
U.S. Ser. No. 07/850,682 filed Mar. 10, 1992, U.S. Pat. No. 5,303,218 Inventor: Atsushi MIYAKE;
U.S. Ser. No. 07/850,684 filed Mar. 10, 1992, pending Inventor: Atsushi MIYAKE;
U.S. Ser. No. 07/871,241 filed Apr. 20, 1992, pending Inventors: Nobuo IIZUKA and Hajime MANABE; and
U.S. Ser. No. 07/965,180 filed Oct. 23, 1992, pending Inventor: Nobuo IIZUKA.
Such digital recorders using memory medium of a random access type can take advantage of such memory device for random-access editing and reproducing recorded digital audio data which is expressed in predetermined data blocks (hereafter called as events) for reproduction.
During recording or reproducing an audio signal, a signal process such as a filtering process is often executed on the audio signal. Further, in the above digital recorder which is capable of editing and reproducing events with use of the above hard disk, it is sometimes required to subject the audio signal expressed in the unit of events to a signal process.
Methods for processing a signal will be considered, such as a process for directly rewriting digital audio data of target events, and a process for processing digital audio data of the target events stored in an area of the memory device (for example, a hard disk) and then storing the resultant data again in other area of the memory device. However, the former process involves such a disadvantage as reserves no original digital audio data while the latter process has a disadvantage that requires much more memory areas because the processed digital audio data must be stored in a memory area other than the memory area where the digital audio data are originally stored.
To solve these disadvantages, a method will be considered which designates, in the editing process of the events, only contents of the signal process to be effected on the digital audio data, and effects the designated contents of the signal process on the original digital audio data, outputting the resultant data.
Recently, digital signal processors (DSP) are in use which are capable of effecting the above signal processing in real time. As a conventional recorder which is capable of processing a signal in a reproducing mode and further in a recording mode, a digital recorder will be considered, in which the DSP is disposed directly before a D/A convertor and directly after an A/D convertor, and which effects a digital signal process on the digital audio data just before D/A conversion or just after A/D conversion.
When the above conventional recorder is applied to a digital recorder in which digital audio data of multiple systems (tracks) are recorded and reproduced simultaneously, there will be possibility of necessity for effecting a different relevant signal process on data of every track. To take countermeasure to meet the above necessity, one DSP must be prepared for each track in the recorder. Even if an arrangement in which one DSP is used in a time sharing manner should be employed in the recorder, different sample of previous digital audio data for every track must be reserved and these samples of previous digital audio data must be controlled to be switched for the signal process, for example, in a digital filtering process in which previous data is used for a signal process. Furthermore, it can be required that a different relevant signal process is effected on a signal of every track. For example, events of the track 1 are subjected to a low pass filtering process, events of the track 2 to a band pass filtering process and events of the track 3 to a sound volume control process. Therefore, control data for effecting a different relevant signal process on a signal of every track must be selectively controlled.
As described above, conventional recorders involve problems that enlargement in a scale of hardware or complicated control of signal processes is inevitable, resulting in increase in manufacturing cost of the digital recorder or in lowered signal processing capacity.